As is well known, a liquid crystal display panel incorporates, in its rear surface, a plurality of discharge tubes serving as a backlight. A recent liquid crystal display panel tends to have a larger screen size. For example, liquid crystal TVs for household use conventionally had a 20-inch screen at most. However, the current mainstream is liquid crystal TVs using 32- to 45-inch liquid crystal display panels. As the size of the liquid crystal display panel becomes larger, the number of discharge tubes per liquid crystal TV largely increases.
FIG. 5 shows a discharge tube driving device according to a prior art which drives a plurality of discharge tubes having pseudo U-tube structures. The discharge tube driving device shown in FIG. 5 basically includes a control circuit 10, a switching circuit 20, and driving transformers T10 to T40.
The switching circuit 20 parallelly applies driving pulses to the primary windings of the driving transformers T10, T20, T30 and T40. The secondary winding of each of the driving transformers T10, T20, T30 and T40 is connected in series to two discharge tubes so as to form a so-called pseudo U-tube structure. A high-frequency driving signal generated in the secondary winding of each driving transformer turns on a corresponding discharge tube.
Japanese Patent Laid-Open Nos. 2005-005059 and 2005-032940 describe discharge tube lighting devices according to prior arts.
In the discharge tube driving device shown in FIG. 5 as a prior art, however, the low-voltage interconnections that connect the discharge tubes are short in the pseudo U-tube structures. To drive eight discharge tubes FL10 to FL80 in FIG. 5, the four driving transformers T10 to T40 are necessary on the board layout. The reason for this is as follows. The positive high-voltage interconnections and the negative high-voltage interconnections on the board cross each other, as indicated by the dotted circles in the circuit diagram of FIG. 6. For this reason, especially in the discharge tube driving device which requires a high voltage to drive the discharge tubes, such a board design is impossible. Hence, as described above, when the size of the liquid crystal display panel becomes larger, the number of discharge tubes required increases. For example, eight or more discharge tubes that form pseudo U-tubes require four or more driving transformers.
In the conventional scheme of the discharge tube driving device shown in FIGS. 5 and 6, the number of driving transformers increases along with the increase in the number of discharge tubes to be used. This also increases the area occupied by the driving transformers, resulting in an expensive and bulky discharge tube driving device.